Patent GB-988858-A (GB)
Title: Signal generator
IPC: H03B23/00
Filed: 1961-07-14
Abstract: 988,858. Radio frequency systems, frequency changing and control circuits. STANDARD TELEPHONES & CABLES Ltd. July 14, 1961 [July 20, 1960], No. 25673/61. Headings H3A, H3F and H4L. A signal generator includes a loop network for the recurrent circulation therein of a signal consisting of alternating current of a predetermined frequency range and duration. Associated with the loop network is a means to initiate the signal, and the signal frequency is progressively changed upon each circulation of the signal through the loop network. The loop network includes time delaying arrangements to delay the signal by a predetermined interval on each circulation and frequency changing arrangements to progressively change the frequency of the signal on each circulation of the signal through the loop. Output arrangements coupled to the network extract the progressively changing frequency. The basic system of the invention is indicated in Fig. 1: a signal from a source 5, which may be a continuous wave oscillator generating a frequency f0, is injected into the loop network 2 when the switch 8 is operated. This signal appears at the output 3 for as long as the switch is closed, and also passes into the delay 9 followed by the frequency changer 10, which produces a new frequency in accordance with a predetermined relationship, this frequency appearing at the output 3 and also being recirculated. Fig. 2, waveform B, indicates the type of output which may be obtained, while waveform C shows a plot of frequency output against time. An amplifier (not shown) may be included in the loop 2 in order to overcome the network attenuation and maintain the output amplitude constant. The operation may be terminated after a desired number of circulations. By varying the type of input from the source 5 and the frequency changes produced in the arrangement 10 many different types of varying frequency output signals may be produced (Fig. 4). Fig. 5 indicates details of one type of generator. The continuous frequency fo from an oscillator 18 is applied through a gate 7a under the control of enabling pulses from a source 19 actuated from a master timing generator 23. The signal is passed via a limiter amplifier 33 and a bandpass filter 34 to the output filter 35 and also to the delay line 24, after which it passes to a mixer 27, where it is mixed with a signal of frequency f1 from an oscillator 28. The resultant signal is filtered by the high bandpass filter 29, which allows frequencies of fo +f1 and greater to be transmitted, and is then mixed with the output from an oscillator 31 of frequency f1-#f. After passing a further high bandpass filter 32 of cut-off frequency slightly less than f0 + #f, the signal is returned to the loop input. The operation of the oscillators 28 and 31 may be controlled by enabling pulses from the source 21, which in turn is controlled by the timer 23. The output from the generator increases by an amount #f for each time interval #t set by the delay line 24, provided that the initial burst of frequency from the oscillator 18 lasts for less than this time. Further embodiments wherein the initiating source may be simply a power supply (Fig. 6, not shown) or a swept oscillator (Fig. 8, not shown) are described. This latter embodiment has the advantage that the rate of frequency increase from the swept oscillator may be the same as that of the desired output, so that the overall output increases smoothly rather than in discrete steps (Fig. 9, not shown). A similar advantage may be obtained by using a sawtooth generator as an initiating source, coupled with a swept oscillator contained in the loop network (Fig. 10). The sawtooth, via the reactance tube 52, causes the oscillator 51 to carry out the initial part of its sweep, which is fed to the output 3d and to the delay 9d and frequency changing means 10d. The output from this is compared with the output from the oscillator 51 in the phase comparator 54, which produces an output when the two frequencies supplied to it are the same. The output activates an integrator 55, which takes over control of the reactance tube 52 and hence the swept oscillator after the initiating sawtooth has terminated, and an output frequency from the system varying linearly with time is maintained. Other modifications of this embodiment are described. The generator may be adapted as a data transmission system capable of handing one or more channels of information. In Fig. 12 pulses from a source of information P are transmitted to the loop network via a gate 7e under the control of enabling pulses from a source 71 actuated from a timing generator 77. A gate 72 in the output is also controlled. Information is inserted into the loop in binary coded form, represented by the presence or absence of signals in sequential time intervals (see waveform A, Fig. 13). The first pulse circulates so that after time #t it is represented by a frequency f+#f. It circulates again together with the second pulse and so on, and the output gate is opened when all the time sequential signals have been inserted into the loop, and the transmitted information contains all the information from the source simultaneously, to be separated by frequency division techniques. A further source Q may provide other pulses which may be represented by a different frequency and transmitted simultaneously with the information from P (as in Fig. 13) or time separated therefrom (Fig. 14, not shown).